Develop Reference

Fragments, How to Navigate back to the previous Fragment, from the current Fragment?

I am using Fragment A,Fragment B .. and so on. i want to navigate back to the previous Fragment, from the current Fragment.
I want to use Back Button in Mobile to get back navigation.
How can i do this ? OR i have to make Back button in layout xml.
i tried below code,
fTransaction.add(R.id.container, nF).addToBackStack(null).commit();
when i pressed Back Button in Mobile , it restarts the App.

To go back to previous fragment using phone's back button you should override onKeyDown() mehtod.
#Override
public boolean onKeyDown(int keyCode, KeyEvent event)
{
if(keyCode == KeyEvent.KEYCODE_BACK)
{
getFragmentManager().popBackStack();
return true;
}
return false;
}

When replacing a fragment use replace instead of add and then addToBackStack:
fTransaction.replace(R.id.container, nF).addToBackStack(null).commit();

Try this:
fTransaction.addToBackStack(null).add(R.id.container, nF).commit();

How to handle back button using view pager?

I am having two fragments Frag A and Frag B which are rendered using view pager .
If user has swiped from A to B then presses back button(when in B) then user should go to A instead of coming out of view pager . How can we achieve this ?
Adding transaction to backstack does not seem to help .
Thanks

You have to override the onKeyDown() method in the Activity.
#Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
myViewPager.setCurrentItem(0, true);
return true;
} else {
return super.onKeyDown(keyCode, event);
}
}
This will capture the "back" button press event and send the user to the first item in the ViewPager.
There is also ViewPager#getCurrentItem() which can be used to go back only if the user swiped. An implementation like this:
#Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK && myViewPager.getCurrentItem() == 1) {
myViewPager.setCurrentItem(0, true);
return true;
} else {
return super.onKeyDown(keyCode, event);
}
}
would send the user back to the previous page only if the user was on the next page. Else, it will register the "back" normally and the user will exit as expected.
You may want the case in which the user goes back to the previous page (assuming you have more than two pages). In which case, you want to implement the ViewPager.OnPageChangeListener() and save the position every time onPageSelected(int position) is called. If you implement them in a stack, then you can pop them off every time the user presses "back". Once the stack is empty, exit the app.
EDIT
As correctly stated in the comments by Jade Byfield, a slightly easier way to do this would be to use onBackPressed() in the Activity. This will only work in API levels 5+.
#Override
public void onBackPressed() {
if(i_dont_want_to_leave) {
myViewPager.setCurrentItem(0, true);
} else {
super.onBackPressed(); // This will pop the Activity from the stack.
}
}

On the Android Docs page
https://developer.android.com/training/animation/screen-slide.html#viewpager
I found an example of handling ViewPager sliding and there's a method
#Override
public void onBackPressed() {
if (mPager.getCurrentItem() == 0) {
super.onBackPressed();
}
else {
mPager.setCurrentItem(mPager.getCurrentItem() - 1);
}
}
This selects a previous page or exits the current activity.

I think a better approach would be to delegate the back key handling to the respective fragments. I have used a CustomFragment which supports a method to handle the back key. All the Fragments will be extending from this CustomFragment.
public abstract class BackKeyHandlingFragment extends Fragment {
public abstract boolean handleBackKey();
}
Activity can delegate the backKey processing to current Fragment. Fragments can perform required actions in their respective implementation of handleBackKey method. The method can return true to tell activity not to process the back key. To go ahead with default back key action at Activity level, the method can return false.
public void onBackPressed() {
BackKeyHandlingFragment fragment = (BackKeyHandlingFragment) mSectionsPagerAdapter.getItem(mViewPager.getCurrentItem());
// Fragment should return boolean according to app requirements after processing back key
if (!fragment.handleBackKey()) {
super.onBackPressed();
}
}

List_view getting items back

I have 3 different function in an activity namely , main category,sub_category and list of items. By clicking main category it displays sub_category and same like list of item.I want to give back option, in order to view back functions. for example at the time of viewing list_of item by clicking back option, i want to show sub_category and by clicking back button from sub_category i want to display main category. I dont know how to do this. All the above function are reside in one class. can anyone give solution for this..??

Override onKeyDown function to handle back key event.
#Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if((keyCode == KeyEvent.KEYCODE_BACK)) {
Log.d(this.getClass().getName(), "back button pressed");
// invoke your navigation function
// return true; - to prevent this event from being propagated further
}
return super.onKeyDown(keyCode, event);
}

Help prevent Back button from closing sub-activity

I have a main activity. It's main purpose is to handle Tab menu. If a user click a tab it'll load another activity as a sub-activity, still showing the tab menu. I am using Intent to do this:
setContent(new Intent(this,B.class))
This sub-activity has an onclick function as well. If the user clicks one of the links it'll load xml layout file using setContentView command:
setContentView(R.layout.B1);
Now, when the back button is pressed while xml file is loaded, it'll close the entire application. Is there a way to prevent this, say, return to the sub-activity or the main activity?
thanks for all your help.

You should override the onBackPressed method in your activity or sub activity:
#Override
public void onBackPressed() {
//TODO Do your task here
}

In your sub activity you should override the fallowing:
#Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) //Override Keyback to do nothing in this case.
{
return true;
}
return super.onKeyDown(keyCode, event); //-->All others key will work as usual
}

Android Back Button functionality

I'm little bit fed up with the device back button functionality.
I have two activities. From 1st I go to 2nd and display one item through array in ListView and when I presses the back button i came back to 1st activity.
when I again go to 2nd activity to display the item once again it showing me the previous items at 1st row and then the same item in the second row as well.
Means it is not removing the previous item when i presses the back button.
I have used:
public void onBackPressed ()
{
for(int i=0; i<sub_categories.length;i++)
{
sub_categories[i]="";
}
Log.d(this.getClass().getName(), "*****************back button pressed");
}

I'm not entirely sure what you are trying to do, since you are not describing where you actually delete your item.
If you really always want to delete the item you have highlighted upon leaving activity no 2, you could delete it in onStop().
If you don't want to remember the state when leaving the activity you should set android:saveEnabled="false" in your layout manifest.

You need to notify the adapter that the data has changed using notifyDataSetChanged. And the adapter will tell the ListView to update it's view.

Here is how you can run code on key press:
#Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
Log.d("BACK KEY PRESSED");
}
return super.onKeyDown(keyCode, event);
}
After returning to an activity, use notifyDatasetChanged in the activity onResume() to update the list.